I just got my hands on an 89 convertible, 61k, great shape, great ride, and I don't want to keep running her on the old gear oils, but I don't have the money to order any right now. (spent it all on the car! lol)

My preference is redline, and I have a bunch of regular 75w90 laying around. If I threw this in there for now, and ran mt90 when I can, would it be a bad idea?

Also I keep reading that 75w90 is fine for the diff, but I remember my friend recomended that I use 140 weight in the diff. Opinions?

 

you're good with 75-90.

 

Well, my question wasn't well worded. I know that using "regular" weights isn't going to be 'damaging' - what I mean to say is; Would they be less protecting? Would mt90 / 140 weight be a better idea?

 

For the rearend, ANY GL5 90wt gear oil will work well.

For the manual, I still recommend a GL4 or dual rated GL4/GL5 fluid. Some straight GL5's and all LSD gear oils aren't optimized for synchro function and life.

IMO, there is no need for 140wt gear oil anywhere in a 'vert.

 

You'll be fine with any old 75-90 for a long while, as long as it's GL-4 and safe for your synchros. GL-5 might dissolve them. For later Redline is good, but Royal Purple Synchromax (www.royalpurple.com) or Neo (www.mazdatrix.com) is better. I read a bunch of user comments on tranny oils: Some oils reduced or removed gear grinding but didn't make shifting any easier. Others made shifting easier but sometimes increased gear grinding - Redline included. Only the two I mentioned both made shifting easier and reduced or removed gear grinding. Royal Purple is supposed to provide a little less friction than the others, too - i.e., slightly more power & mpg. I use Neo and now my shifter works as easy as a children's toy.

 

A good synthetic is necessary, just recommended. At 61k miles, your tranny's probably in pretty good shape so don't worry about it. Just get some nice synthetic in there whenever you can afford it.

 

RoyalPurple synchromax is too thin for the RX7 transmission. You need a 90wt gear oil and not a 20wt ATF-substitute. If RP is your brand, Maxgear 75w90 can be used both in the tranny and rearend. Maxgear did not shift as well as Redline MT90 in my transmission.

 

i say redline all the way! very good stuff

 

Oh, believe me, I'm religious with redline. All the 75-90 I have is Redline. I just happened to have like three gallons of it hanging around from a "bulk purchase" for my toyota truck. I also had a single quart of mt90 hanging around on the shelf. So I threw that one mt90 into the tranny and filled the rest with the regular redline 75-90, and of course the differential too.

Yeah, a lot of honda-heads have told me "just go to kragen and get royal purple"

For that very reason, I avoid royal purple.

On a side note....


You know, it's funny. I'd run my 88 vert with regular GTX motor oil, and every oil change, the oil was still a crisp golden. (too bad the damn thing had a bad water seal!!!) And the gear oils, when I dumped the old ones it came with, were also a nice golden still. This s5 I have now, despite looking and running so much better, had really dirty tranny and motor oil. The diff oil was still hella clean though. Well, we'll see when I change my own oils, what they look like.